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I've seen the solar noon formula described as snoon = 720 – 4*longitude – eqtime. I'm curious if it is equally reliable within a relatively small margin of error (+-60 seconds) to simply get the midpoint between sunrise and sunset, given that data is already calculated and available.

Is there any occasion when solar noon wouldn't be equal time from sunrise and sunset, give or take the aforementioned margin of error?

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The approach of using the midpoint of the sunrise and sunset times is reasonably accurate. I do not know what the accuracy is, but probably within 1 or 2 minutes. It would not be as accurate in polar regions where the sun is close to being visible all day.

The main reason it is not precise is that the sun is moving north (December through June) or south. This changes the time of sunset with respect to sunrise if the Sun were not moving north or south. Solar noon would be earlier or later, respectively, from the midpoint.

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